Middleware

A Middleware runs code before and/or after route resolution, for every request whose path matches its pattern. Like Route, it extends Pattern (see Route patterns), so it has a pattern and a priority.

Defining a middleware

import { Middleware } from '@chialab/synapse';

const logger = new Middleware({
    pattern: '*',
    priority: 100,
    before: (request, response, params, router) => {
        console.log('navigating to', request.path.href);
    },
    after: (request, response, params, router) => {
        console.log('rendered', response.title);
    },
});

before (MiddlewareBeforeHandler) runs before any route is matched.
after (MiddlewareAfterHandler) runs after a route has produced a response.
Both receive (request, response, params, router), where params are the values extracted by matching the middleware's own pattern against the current path (independent of any route's params).
Either hook can return a new Response (or mutate and return the given one) to replace what continues through the pipeline; returning nothing keeps the current response. Calling response.redirect(path) from a hook short-circuits the rest of the pipeline in favor of a replace() to path.

Connecting a middleware

Directly on a Router:

router.middleware(logger);
// or inline:
router.middleware('*', undefined, (request, response) => {
    /* before */
});

Or declared statically on an App:

class DemoApp extends App {
    static middlewares = [logger, new DocumentMetaMiddleware()];
}

Connected middlewares are sorted by descending priority (default 20) and, for each request, Router#handle runs every matching middleware's before hook (highest priority first), then the matched route, then every matching middleware's after hook.

`DocumentMetaMiddleware`

A built-in middleware that keeps document.title and <meta> tags in sync with the current Response's title and meta:

import { DocumentMetaMiddleware } from '@chialab/synapse';

class DemoApp extends App {
    static middlewares = [new DocumentMetaMiddleware()];
}

Its constructor is (doc = document, titleBuilder?, metaBuilder?):

titleBuilder: (title: string | undefined, response: Response) => string — defaults to (title) => title || ''; use it to add a suffix, e.g. (title) => title ? ${title} · My App : 'My App'.
metaBuilder: (meta: Meta | undefined, response: Response) => Meta — defaults to (meta) => meta || {}; use it to inject metadata shared across pages.

On its hookAfter, it calls the builders with response.title/response.meta and writes the result to the document: existing <meta name="..."> tags are updated in place, new ones are appended to <head>, and tags that are no longer present in the new Meta object are removed.

new DocumentMetaMiddleware(document, (title) => (title ? `${title} · Demo` : 'Demo'), (meta) => ({
    ...meta,
    'og:site_name': 'Demo',
}));

Set response.setTitle(...) and response.setMeta(...) from your route handlers (see Request & Response) — DocumentMetaMiddleware only reads and applies them.

Middleware ​

Defining a middleware ​

Connecting a middleware ​

DocumentMetaMiddleware ​

Middleware

Defining a middleware

Connecting a middleware

`DocumentMetaMiddleware`